Should all parts of a physical object be modelled as a single Blender object?
There's a question you need to answer before asking: 'How do I draw this stool?'.
It's: 'Why am I drawing this stool?'.
If you're using a CAD package, the answer to the latter is usually given. It's to propose, or to aid, the manufacture of a real-world stool. But if you're using a visualizaton and animation suite like Blender, that's not the case.
It could be:

A stool to illustrate the assembly of stools, including the deployment of screws
A 3D-printable stool, with a manifold surface.
A pre-lit low-poly stool, for use in a limited-resources game
A hero foreground stool, with wood grain and shiny screw heads, in an
architectural visualization, or product shot.
A graphic stool, for use in a poster advertising a chain of cafés
A hacked out-of-focus background stool, only half of which is ever seen
A toon stool, which can run away from its obese owner, and attempt suicide by jumping out of an apartment window
A stool for sale as an asset to be used by other people, whose purpose is part of its advertised specification, and needs to be by-the-book
A photorealistic VFX stool, which will need to bounce off a previously filmed floor, and be shot to pieces in scene 23
.......

These are considerations unlikely to be taken into account by a CAD user. There's no single paradigm. Each stool will require a different approach to serving its purpose, while avoiding as much work as possible.